Garrulus Glandarius) Prefer Oaks and Acorns in Central Europe
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Ornis Hungarica 2020. 28(1): 169–175. DOI: 10.2478/orhu-2020-0010 Foraging Eurasian Jays (Garrulus glandarius) prefer oaks and acorns in central Europe Cezary MITRUS1,* & Josif SZABO2 Received: December 14, 2019 – Revised: February 17, 2020 – Accepted: February 18, 2020 Mitrus, C. & Szabo, J. 2020. Foraging Eurasian Jays (Garrulus glandarius) prefer oaks and acorns in central Europe. – Ornis Hungarica 28(2): 169–175. DOI: 10.2478/orhu-2020-0010 Abstract The Eurasian Jay (Garrulus glandarius) is considered as the most important factor in the dispersal and spread of oak species. We conducted studies in oak stands in four coun- tries (Poland, Hungary, Romania, Ukraine) in the autumn of 2015 and 2016. To identify the preferences of Jays for both acorns and trees, we compared the size of acorns and tree characteristics between each selected tree and the closest unused oak. We found that acorns from selected oaks were smaller (narrower) than those from unused trees. We found no differences in the characteristics of selected and unused oaks. These results indicate that the size of acorns can be an important indicator determining the choices of foraging birds. The Jays’ preferences for specific trees may influence the composition of oak populations. Trees with certain phenotypic and genomic char- acteristics may be favoured and dominate in the ecosystem. Keywords: dispersion, trees, birds, preferences, coevolution Összefoglalás A szajkó (Garrulus glandarius) a legfontosabb faktornak tekinthető a tölgyfajok terjedésében. Vizs- gálatainkat négy ország (Lengyelország, Magyarország, Románia, Ukrajna) tölgyeseiben végeztük 2015 és 2016 őszén. A szajkók tölgyfa és makk preferenciáinak vizsgálatához összehasonlítottuk a szajkók által választott fák és azok makkjainak jellemzőit a legközelebbi, nem választott tölgyfával és annak makkjaival. A madarak által válasz- tott makkok kisebbek (keskenyebbek) voltak a nem választott fák makkjaihoz képest. Más vizsgált jellemzőben nem találtunk különbséget a választott és nem választott tölgyfák között. Az eredmények rámutatnak arra, hogy a makkok mérete fontos indikátor lehet a madarak táplálékválasztásában. A szajkók preferenciái kihathatnak a tölgyállomá- nyok összetételére. Bizonyos feno-, illetve genotípusú fák kedveltebbek lehetnek, így uralhatják az ökoszisztémát. Kulcsszavak: diszperzió, fák, madarak, preferenciák, koevolúció 1 Department of Vertebrate Ecology and Paleontology, Institute of Biology, Wrocław University of Environmental and Life Sciences, Chełmońskiego 38c, 51-631 Wrocław, Poland 2 Str.Croitorilor 2/49, Odorheiu Secuiesc/Harghita 535600, România * corresponding author Introduction Animals are required for dispersing the seeds of many plant species in both the tropics and in temperate zones (Howe & Smallwood 1982, Jordano 2000). Based on the way in which seeds are transported, three categories of zoochory are usually distinguished: endozoocho- ry – seeds are ingested by an animal and later regurgitated or defecated, epizoochory – seeds are accidentally attached to the outside of an animal body, for example, in the fur, and synzoochory – animals actively transport seeds and deposit them elsewhere (Jordano 2000, Hulme 2002, Will & Tackenberg 2008, Vander Wall & Beck 2012). In particular, birds play an important role in plant dispersion over long distance and this is a good example of 170 ORNIS HUNGARICA 2020. 28(1) synzoochory. In many cases, a very close association between animals and plants can be considered as coevolution (Pons & Pausas 2007). Mutualism, being advantageous both for birds and plants, is also observed (Pesendorfer et al. 2016). Thus, such a coexistence gives the opportunity to study relationships between birds and plants. The Eurasian Jay (Garrulus glandarius) is considered the most important factor in the dispersal and spread of oak Quer cus species (Bossema 1979, Clayton et al. 1996, Perea et al. 2011, Kurek et al. 2018). Long distance dispersal of acorns is possible due to the ability of Jays to collect, carry and cache seeds in the ground (Bossema 1979, Mosandl & Kleinert 1998, Pons & Pausas 2007, Kurek & Dobrowolska 2016). Birds are selective and choose acorns for hoarding by visual means, mainly according to the colour and size (Bossema 1979, Pons & Pausas 2007, Richardson et al. 2013, Bieberich 2016). However, few studies addressed the selection of acorns by Jays (Bossema 1979, Pons & Pausas 2007, Myczko et al. 2014, Bieberich 2016) and knowledge on the characteristics of trees selected for foraging is lacking. The aim of this study was to determine the foraging preferences of Jays in relation to the characteristics of oaks and acorns in central Europe. We tested the following hypotheses: Jays collect acorns from specific trees, oaks and acorns selected by birds differ from unused trees, location (country) does not influence the characteristics of trees and acorns. Materials and methods Study area Observations were made in four countries (Poland, Hungary, Romania, Ukraine) in oak stands on lower (250–450 m above sea level) parts of the Carpathian region. In Poland, the studies were conducted in the oak forest near Kalwaria Pacławska (49°38’44.5”N, 22°41’48.5”E) – 30 ha, in Hungary in the Bükk National Park in the vicinity of Cserépfa- lu (E 47°58’00.0”N, 20°33’47.6”E) – 20 ha, in Ukraine close to Ivanivka (48°53’18.0”N 24°06’03.1”E) – 30 ha and in Romania near Homoródújfalu (46°07’50.8”N 25°24’56.1”E) – 20 ha. In the cases of Romania and Hungary, the oak stands were within pasture with the trees usually (only oaks) growing at low density. Herds of cattle and sheep grazed beneath the trees. In the case of Hungary, turkey oaks (Quercus cerris) dominated in the stands with only single individuals of pedunculate oak (Quercus robur), also present. In Poland and Ukraine, trees in abandoned (20–30 years ago) wood-pastures had expand- ed to produce mixed forest, where beside stands of pedunculate oak, there were also stands of other trees: hornbeam (Carpinus betulus), beech (Fagus sylvatica), sycamore (Acer pseu doplatanus), small-leaved lime (Tilia cordata), norway spruce (Picea abies), European sil- ver (Abies alba) and in the lower layers, common hazel (Corylus avellana). Field data collection The observations were carried out in two autumn seasons (2015 in Poland and Ukraine, 2016 in Hungary and Romania) in October and November. The total observation time C. Mitrus & J. Szabo 171 amounts 42 days (20 days in 2015 and 22 days in 2016). Trees used by birds were locat- ed in oak stands or pastures with solitary trees by observations of flying Jays. Only oaks where foraging Jays were observed at least twice were used in the analysis. The follow- ing information was then collected: characteristics of the selected tree (species, trunk cir- cumference at height of 1.5 m, height of tree, radius of crown) and habitat characteristics (inside forest or in open area in the case of solitary oaks). The same characteristics were recorded for the nearest oak with acorns but not used by Jays. In the case of open areas, only unused oaks within 20 m were included in analysis. Additionally, the characteris- tics of fallen acorns under oaks were described. From the ground under each used and the closest unused oak, 50 randomly selected (without signs of infestation by insects) acorns were collected. After drying in the laboratory, they were measured using sliding callipers by one person (CM) recording length and width (in mm). Statistical analyses For comparisons of two groups of data the Mann–Whitney U test was used. To determine factors affecting the Jay’s choice, Generalized Linear Model (GLM) with binominal dis- tribution and logit function were constructed where: biometric traits of acorns and country (place of observation) were used as independent factors. Because of the number of data, this model was used only in the case of pedunculate oaks. All statistical analyses were undertak- en using Statistica for Windows v.13.3. Results Jays used two species of oaks: Quercus robur in the studies in Poland, Ukraine and Ro- mania, and Q. cerris in the case of study in Hungary. In total, 421 visits of Jays were ob- served. We characterised 25 (5 from Ukraine, 6 from Poland, 6 from Romania and 8 from Hungary) used and 12 unused oaks (3 from Ukraine, 2 from Poland, 3 from Romania and 4 from Hungary). We did not find differences in the parameters (height, size of crown and diameter of trunk) of selected and unused trees (Table 1). The oaks which were used by foraging Jays in open areas were significantly shorter in height and had bigger crowns Table 1. Characteristics of oaks selected and unused by Jays 1. táblázat A szajkók által használt és nem használt tölgyek jellemzői Selected Unused NN Mean Min-Max Sd N Mean Min-Max Sd U test, p -0.69, Height (m) 25 22.7 14–30 4.81 12 24.2 19–31 4.38 p=0.49 -0.42, Crown (m) 25 7.8 4.7–12.4 2.30 12 7.8 6.0–11.1 1.32 p=0,67 0.08, Circumference (cm) 25 217.2 129–430 83.10 12 216.4 119–345 82.79 p=0.93 172 ORNIS HUNGARICA 2020. 28(1) than those growing in the forest (Table 2). Place (country) of observation and size (width but not length) influenced the selection of Jays in the case of Q. robur (Table 3, 4). The size of acorns also depended on oak species. Acorns of Q. cerris were significantly longer and wider than those from Q. robur (Table 5). Table 2. Comparison of oaks growing in two different habitats 2. táblázat A tölgyfák jellemzőinek összehasonlítása nyílt és zárt állományban Open area Forest N Mean Min-Max Sd N Mean Min-Max Sd U test, p 2.80, Height (m) 25 18.8 14.0–30.0 5.26 12 24.5 19.0–31.0 3.64 p<0.01 -1.95, Crown (m) 25 8.8 4.7–12.0 2.12 12 7.4 5.1–12.4 1.88 p<0.05 -0.79, Circumference (cm) 25 224.3 120–430 82.52 12 18.75 119–330 83.00 p=0.43 Table 3.